A LED filament arrangement

Abstract

The invention provides a LED filament arrangement comprising a printed circuit board and at least one flexible LED filament having a respective length and providing, in operation, LED filament light; wherein the printed circuit board comprises: a front surface arranged on a first side of the printed circuit board; a back surface arranged on a second side of the printed circuit board, the second side being opposite to the first side; an electronic circuit arranged on the front surface of the printed circuit board and configured to convey, in operation, power to the at least one flexible LED filament; at least one opening extending through the printed circuit board from the first side to the second side; wherein each flexible LED filament of the at least one flexible LED filament extends through one or two openings of the at least one opening; wherein each flexible LED filament of the at least one flexible LED filament is partly arranged on the second side of the printed circuit board; wherein each flexible LED filament of the at least one flexible LED filament is mechanically and electrically connected to the electronic circuit on the front surface of the printed circuit board.

Description

[0001] A LED filament arrangement

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a LED filament arrangement and a corresponding lamp or luminaire comprising such a LED filament arrangement.

[0004] BACKGROUND OF THE INVENTION

[0005] LED based lighting devices have revolutionized the global lighting market. LED based lighting provides, for example, an improved efficiency related to the ratio of light energy and heat energy, a reduced power consumption, and a longer operational life. Due to such advantageous aspects, conventional lighting devices are rapidly being replaced by LED based lighting devices. This replacement is also called retrofitting.

[0006] It is moreover observed that users appreciate retaining the look and feel of an incandescent bulb. Hence, the global lighting market has seen a steep rise of the concept of LED filaments, which are also highly decorative. LED filaments are therefore being used in many retrofit bulbs.

[0007] However, next to retrofit bulbs, LED filaments are also increasingly being used as the primary light source in luminaires as such. Due to the wide application of LED filaments, said LED filaments - or LED filament arrangements - need to be even further improved concerning light distribution, miniaturization, modularity, thermal efficiency, and / or aesthetic properties.

[0008] SUMMARY OF THE INVENTION

[0009] It is an object of the invention to provide an improved LED filament arrangement, which at least alleviates the problems and disadvantages mentioned above. Thereto, the invention is defined by the appended claims. Thereto, the invention provides, a LED filament arrangement comprising a printed circuit board and at least one flexible LED filament having a respective length and providing, in operation, LED filament light; wherein each flexible LED filament comprises a respective main part extending between a first end and a second end; wherein the printed circuit board comprises: a front surface arranged on a first side of the printed circuit board; a back surface arranged on a second side of the printed circuit board, the second side being opposite to the first side; an electronic circuit arranged on the front surface of the printed circuit board and configured to convey, in operation, power to the at least one flexible LED filament; at least one opening extending through the printed circuit board from the first side to the second side; wherein each flexible LED filament (of the at least one flexible LED filament) extends through one opening or two openings of the at least one opening; wherein the respective main part of each flexible LED filament (of the at least one flexible LED filament) is partly arranged on the second side of the printed circuit board; wherein the first end and the second end of each flexible LED filament (of the at least one flexible LED filament) are mechanically and electrically connected to the electronic circuit on the front surface of the printed circuit board.

[0010] Hence, the present invention provides a LED filament arrangement wherein the printed circuit board comprises a front surface arranged on a first side and a back surface arranged on second side opposite to the first side. The least one flexible LED filament is at least partly arranged on the second side of the printed circuit board.

[0011] Since the least one flexible LED filament is partly arranged on the second side of the printed circuit board, extends through the at least one opening from the first side to the second side of the printed circuit board, and is mechanically and electrically connected to the electronic circuit on the front surface of the printed circuit board, the LED filament arrangement according to the present invention advantageously separates the illumination function of the LED filament arrangement from electronical and mechanical functions.

[0012] Hence, the LED filament arrangement according to the present invention improves the light distribution and aesthetic appearance of the flexible LED filaments on the second side, because the second side of the printed circuit board only exposes the flexible LED filaments and not the electronic circuit or mechanical connections arranged for powering said flexible LED filaments.

[0013] Moreover, the LED filament arrangement according to the invention facilitates modularization and assembly as the electronic circuit and mechanical connections are all confined to the first side of the printed circuit board.

[0014] Yet even further, while electrical and mechanical features of the LED filament assembly can be arranged on the front surface and first side, the second surface and the second side provide freedom to design a layout for the flexible LED filaments that may solely be dedicated to the light distribution in on-state and the visual appearance in off-state of the LED filament arrangement. As mentioned, each flexible LED filament according to the invention may comprise a main part, a first end and a second end, wherein the main part is extending between a first end and a second end, wherein the main part of the flexible LED filament is partly arranged on the second side of the printed circuit board, and wherein the first end and the second end are partly arranged on the first side of the printed circuit board, and wherein the first end and the second end are configured to mechanically and electrically connect the flexible LED filament to the electronic circuit on the front surface of the printed circuit board.

[0015] In a related example, the at least one opening comprises a first opening and a second opening, wherein the first end of the flexible LED filament extends through said first opening, and wherein the second end of said flexible LED filament extends through said second opening.

[0016] In an embodiment, the LED filament arrangement according to the invention is provided, wherein the at least one flexible LED filament comprises a number of N flexible LED filaments; wherein the at least one opening comprises between N and 2*N openings. In an embodiment, N > 3. For example, N may be N=3.

[0017] For example, considering the number of N being N = 1, a single flexible LED filament is provided. Also considering that only one opening is provided according to the invention, then said single flexible LED filament may extend through only one opening twice, such that a first end and a second end of the flexible LED filament may be connected to the electronic circuit at the first side of the printed circuit board.

[0018] In an embodiment, said at least one opening is at least one through-hole. In an embodiment, said at least one opening is at least one slit. Hence, the printed circuit board may comprise at least one through-hole, and / or at least one slit, extending through the printed circuit board from the first side to the second side.

[0019] Said slit may alternatively be phrased as a cut. Said at least one slit may be arranged at a circumference of the printed circuit board. Hence, in examples, said slit may alternatively be an indentation.

[0020] As mentioned, each flexible LED filament has a respective length. In an embodiment, at least 70% of the respective length of each flexible LED filament of the at least one flexible LED filament is arranged on the second side of the printed circuit board. For example, at least 80% of the respective length of each flexible LED filament of the at least one flexible LED filament may be arranged on the second side of the printed circuit board. As mentioned, each flexible LED filament has a respective length. In an embodiment, at least 5% of the respective length of each flexible LED filament of the at least one flexible LED filament is arranged on the first side of the printed circuit board. For example, at least 10% of the respective length of each flexible LED filament of the at least one flexible LED filament may be arranged on the first side of the printed circuit board. In aspects, at most 20% of the respective length of each flexible LED filament of the at least one flexible LED filament may be arranged on the first side of the printed circuit board.

[0021] In an embodiment, the back surface comprises a higher reflectivity for the LED filament light than the front surface of the printed circuit board. In an embodiment, the back surface comprises a light reflectance value (of the LED filament light) of at least 80%, such as for example at least 85%. This renders an improved efficiency of the LED filament light being coupled out from the LED filament arrangement, in operation. For example, in an embodiment, a difference in reflectivity between the first surface and the second surface is at least 5%, preferably at least 10%, and most preferably at least 20%. This counteracts undesired stray light emanating from the at least one flexible LED filament.

[0022] In an embodiment, the back surface is diffusely reflective. This renders no specular reflection of the LED filament light, making the flexible LED filaments better visible, in operation.

[0023] In an embodiment, the printed circuit board is a metal core printed circuit board (MCPCB). Such an embodiment is advantageous, as the metal core printed circuit board provides improved thermal performance and mechanical stability.

[0024] In an embodiment, wherein the electronic circuitry comprises a Driver on Board (DoB).

[0025] In an embodiment, the LED filament arrangement comprises at least one module arranged on the front surface of the printed circuit board; wherein the at least one module is mechanically and electrically connected to the electronic circuit on the front surface of the printed circuit board; wherein the at least one module comprises one or more of: a driver, a controller, a communications module, and / or a sensor.

[0026] Hence, differently phrased, the LED filament arrangement comprises at least one of: a driver, a controller, a communications module, and a sensor; wherein said driver, controller, communications module and / or sensor are arranged on the front surface of the printed circuit board.

[0027] As mentioned, each flexible LED filament has a respective length. In an embodiment, at least 80% of the respective length of each flexible LED filament of the at least one flexible LED filament is arranged on the second side of the printed circuit board and in between the back surface and a virtual plane parallel to said back surface; wherein said virtual plane is at an offset distance of at most 60 millimetres from the back surface.

[0028] In a further embodiment, the at least one flexible LED filament comprises a plurality of curves in a plane parallel to the back surface, wherein each curve comprises an angle of curvature of at least 45 degrees.

[0029] In an embodiment, at least one portion of the LED filament has a curved shape and is arranged at a spacing equal to or larger than 10 mm from the second surface.

[0030] In an embodiment, each flexible LED filament of the at least one flexible LED filament is mechanically and electrically connected to the electronic circuit at respective connection locations on the front surface of the printed circuit board; wherein each of said respective connection locations is within a respective distance D from an opening of the at least one opening; wherein said distance D is equal to at least a factor two and at most a factor ten of a diameter of the respective flexible LED filament of the at least one flexible LED filament. Said diameter may alternatively be a width of a respective flexible LED filament.

[0031] In an embodiment, the at least one opening comprises a cross-sectional area, wherein the cross-sectional area of each opening of the at least one opening is at least a factor 1.05 and at most a factor 4 of a cross-sectional area of the respective flexible LED filament of the at least one flexible LED filament.

[0032] In an embodiment, the printed circuit board has a largest dimension, PCBld, wherein the at least one opening comprises a first opening and a second opening, wherein the first opening and the second opening are spaced apart at a gap distance, G, in a range from 0.2*PCBld to 0.8*PCBld.

[0033] In an embodiment, said cross-sectional shape of the at least one opening is one of: a circle, a square, a rectangle, a triangle, or a polygonal shape.

[0034] In an embodiment, the LED filament arrangement comprises a housing having a light exit window and accommodating the printed circuit board, wherein the second side of the printed circuit board is facing the light exit window.

[0035] In aspects, (at least 80% of) the respective main part of each flexible LED filament of the at least one flexible LED filament is arranged substantially parallel to the printed circuit board. For example, each flexible LED filament of the at least one flexible LED filament may be arranged on the printed circuit board. Each flexible LED filament of the at least one flexible LED filament may abut the printed circuit board. Hence, in embodiments, at least 80% of the length of each flexible LED filament of the at least one flexible LED filament may be arranged parallel to the printed circuit board.

[0036] It is further an object of the invention to provide an improved lamp or luminaire, which at least alleviates the problems and disadvantages mentioned above. Thereto, the invention provides a lamp or a luminaire comprising at least one LED filament arrangement according to any one of the preceding claims. Said luminaire may for example be a spotlight or a downlight.

[0037] In a first paragraph, the invention provides, a LED filament arrangement comprising a printed circuit board and at least one flexible LED filament having a respective length and providing, in operation, LED filament light; wherein the printed circuit board comprises: a front surface arranged on a first side of the printed circuit board; a back surface arranged on a second side of the printed circuit board, the second side being opposite to the first side; an electronic circuit arranged on the front surface of the printed circuit board and configured to convey, in operation, power to the at least one flexible LED filament; at least one opening extending through the printed circuit board from the first side to the second side; wherein each flexible LED filament (of the at least one flexible LED filament) extends through one opening or two openings of the at least one opening; wherein each flexible LED filament (of the at least one flexible LED filament) is partly arranged on the second side of the printed circuit board; wherein each flexible LED filament (of the at least one flexible LED filament) is mechanically and electrically connected to the electronic circuit on the front surface of the printed circuit board.

[0038] BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The invention will now be further elucidated by means of the schematic nonlimiting drawings:

[0040] Fig. 1 depicts schematically an embodiment of a LED filament arrangement according to the invention;

[0041] Fig. 2 depicts schematically an embodiment of a LED filament arrangement according to the invention;

[0042] Fig. 3 depicts schematically an embodiment of a luminaire according to the invention; Fig. 4 depicts schematically an embodiment of a LED filament arrangement according to the invention;

[0043] Fig. 5 depicts schematically an embodiment of a LED filament arrangement according to the invention.

[0044] Fig. 6 depicts schematically an embodiment of a LED filament arrangement according to the invention.

[0045] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] Due to their increased implementation in various applications, LED filaments - or LED filament arrangements - need to be even further improved concerning light distribution, miniaturization, modularity, thermal efficiency, and / or aesthetic properties.

[0047] A LED filament is providing LED filament light and comprises a plurality of light emitting diodes (LEDs) arranged in a linear array. Preferably, the LED filament has a length L and a width W, wherein L>5W. The LED filament may be arranged in a straight configuration or in a non-straight configuration such as for example a curved configuration, a 2D / 3D spiral or a helix. Preferably, the LEDs are arranged on an elongated carrier like for instance a substrate, that may be rigid (made from e.g. a polymer, glass, quartz, metal or sapphire) or flexible (e.g. made of a polymer or metal e.g. a film or foil).

[0048] In case the carrier comprises a first major surface and an opposite second major surface, the LEDs are arranged on at least one of these surfaces. The carrier may be reflective or light transmissive, such as translucent and preferably transparent.

[0049] The LED filament may comprise an encapsulant at least partly covering at least part of the plurality of LEDs. The encapsulant may also at least partly cover at least one of the first major or second major surface. The encapsulant may be a polymer material which may be flexible such as for example a silicone. Further, the LEDs may be arranged for emitting LED light e.g. of different colours or spectrums. The encapsulant may comprise a luminescent material that is configured to at least partly convert LED light into converted light. The luminescent material may be a phosphor such as an inorganic phosphor and / or quantum dots or rods. The LED filament may comprise multiple sub-filaments.

[0050] Figure 1 depicts schematically, by non-limiting example, a LED filament arrangement 10 according to the invention. The LED filament arrangement 10 comprises at least one flexible LED filament 11, 12. Here, for explanatory purposes, the LED filament arrangement 10 comprises two flexible LED filaments 11, 12, namely a first flexible LED filament 11 and a second flexible LED filament 12. Hence, the at least one LED filament comprises a number ofN=2 flexible LED filaments. Said number may alternatively be any other integer number N. The flexible LED filaments 11, 12 are arranged to provide, in operation, LED filament light. The LED filament light may comprise a lighting characteristic, such as a color temperature.

[0051] Here, each of the at least one flexible LED filament 11, 12 is of the same type. This may mean that the color spectrum of the outputted LED filament light of the flexible LED filaments may be the same. Alternatively, the flexible LED filaments may be different, for example of a different type. Namely, in alternative examples, the at least one flexible LED filament according to the invention is a plurality of flexible LED filaments, wherein at least two of the plurality of flexible LED filaments is different. This may mean that the color spectrum of the outputted light filament light of the flexible LED filaments may be different.

[0052] Referring to figure 1, the LED filament arrangement 10 according to the invention comprises a printed circuit board 13 (PCB). Albeit optionally, the printed circuit board may for example be a metal core printed circuit board (MCPCB). The printed circuit board 13 according to the invention comprises a front surface 14 and a back surface 15. The front surface 14 is arranged on a first side 1 of the printed circuit board 13. The back surface 15 is arranged on a second side 2 of the printed circuit board 13. The second side 2 is thereby opposite to the first side 1.

[0053] Still referring to figure 1, the printed circuit board 13 comprises an electronic circuit 16. The electronic circuit is configured to convey, in operation, power to the at least one flexible LED filament 11, 12. The electronic circuit 16 is arranged on the front surface 14 of the printed circuit board 13. In examples, phrased differently, the electronic circuit is confined to the front surface 14.

[0054] Albeit optionally, the electronic circuit 16 comprises a driver 19. This may for example be a Driver on Board (DoB). Albeit optionally, the LED filament arrangement 10 - for example as part of the electronic circuit - comprises a controller 17. This may be a microprocessor. Albeit optionally, the LED filament arrangement 10 - for example as part of the electronic circuit - comprises a sensor 18. This may for example be a light sensor, a temperature sensor, a microphone, a voltage sensor, GPS receiver, and / or a radio (sensor) for performing communication and / or radiofrequency-based sensing. Albeit optionally, not depicted, the LED filament arrangement - for example as part of the electronic circuit - may comprises a communication module. The communication module may for example be a radio module, or for example a Bluetooth, ZigBee, and / or a Wi-Fi chip, such as a Bluetooth- ZigBee combo chip. Yet alternatively, the communication module may comprise a radiofrequency transceiver, for example for cellular communication.

[0055] The printed circuit board 13 further comprises at least one opening 4, 5, 6, 7 extending through the printed circuit board 13 from the first side 1 to the second side 2. Here, this opening is a through-hole. Alternatively, said opening may be a slit. Yet alternatively, said opening may be a slit arranged at the circumference of the printed circuit board, such as an indentation.

[0056] Still referring to figure 1, the through-hole 4, 5, 6, 7 comprises a circular cross-sectional shape. In alternative embodiments, said cross-sectional shape may be polygonal, square, triangular, elliptical, and / or star shaped. In aspects, such a star shaped through-hole may also serve to clamp a flexible LED filament protruding therethrough. In other alternative aspects, the printed circuit board may comprise a protrusion protruding (or: extending) partly in the opening (i.e. e.g. the circular through-hole), wherein said protrusion is configured to (releasably) fixate (or: clamp) the flexible LED filament inside the opening (i.e. e.g. the circular through-hole). Yet even further, in other alternative aspects, an (inner) surface of the through-hole may comprise a higher surface roughness value relative to the front surface and the back surface, wherein the surface roughness value is suitable to maintain a flexible LED filament substantially stationary within said through-hole.

[0057] Still referring to figure 1, according to the present invention, each flexible LED filament 11, 12 of the at least one flexible LED filament 11, 12 extends through two openings of the at least one opening 4, 5, 6, 7. More specifically, the first flexible LED filament 11 extends through a first opening 4 and a second opening 5 in the printed circuit board 13, and the second flexible LED filament 12 extends through a third opening 6 and a fourth opening 7 in the printed circuit board 13. Alternatively, each flexible LED filament of the at least one flexible LED filament may extend through one opening of the at least one opening, thereby having flexible LED filaments sharing an opening.

[0058] Still referring to figure 1, each flexible LED filament 11, 12 of the at least one flexible LED filament 11, 12 is partly arranged on the second side 2 of the printed circuit board 13. More specifically, each flexible LED filament 11, 12 of the at least one flexible LED filament 11, 12 comprises a respective length. Here, at least 70% of the respective length of each flexible LED filament 11, 12 is arranged on the second side 2 of the printed circuit board 13. Hence, the majority of the flexible LED filaments is arranged on the second side 2 and the back surface 15. Here, albeit optionally and not necessary, the first flexible LED filament 11 and the second flexible LED filament 12 comprise a plurality of curves in a plane parallel to the back surface, wherein each curve comprises an angle of curvature of at least 45 degrees. Hence, the at least one flexible LED filament 11, 12 may meander in a plane parallel to the back surface 15. This renders that different optical patterns may be achieved for the LED filament light emanating from the LED filament arrangement.

[0059] More specifically, here, each flexible LED filament 11, 12 of the at least one flexible LED filament 11, 12 is arranged in between the back surface 15 and a virtual plane 9 parallel to said back surface. Said virtual plane 9 may be at an offset distance from the back surface 15. The offset distance may for example be related to the thickness (or: diameter, or: width) of the flexible LED filament 11, 12. For example, the offset distance may be at least four times the thickness (or: diameter, or: width) of a flexible LED filament of the at least one LED filament.

[0060] Here, albeit optionally, the back surface 15 has advantageously a higher reflectivity for the LED filament light than the front surface 14 of the printed circuit board 13, such that the LED filament light may be more efficiently emitted from the LED filament arrangement 10. Yet even further, in examples, the back surface may be diffusively reflective. Alternatively, at least 80% of the respective length of each flexible LED filament may be arranged on the second side 2 of the printed circuit board 13.

[0061] Yet even further, still referring to figure 1, each flexible LED filament 11, 12 of the at least one flexible LED filament 11, 12 is mechanically and electrically connected to the electronic circuit 16 on the front surface 14 of the printed circuit board 13.

[0062] Hence, the present invention provides a LED filament arrangement 10 wherein the printed circuit board 13 comprises a front surface 14 arranged on a first side 1 and a back surface 15 arranged on second side 2 opposite to the first sidel.

[0063] Still referring to figure 1, each flexible LED filament 11, 12 of the at least one flexible LED filament 11, 12 is mechanically and electrically connected to the electronic circuit 16 at respective connection locations on the front surface 14 of the printed circuit board 13. For convenience, only the respective connection locations associated with the first flexible LED filament 11 are depicted in figure 1. Namely, the first flexible LED filament 11 comprises a first end connected to the electronic circuit 16 at a first connection location 61 and a second end connected to the electronic circuit 16 at a second connection location 71.

[0064] Here, each of said respective connection locations 61, 71 is within a respective distance D from the respective openings 6, 7 where the first flexible LED filament 11 is extending through. More specifically, said distance D is equal to at least a factor two and at most a factor ten of a diameter of the respective flexible LED filament of the at least one flexible LED filament. In other words, the flexible LED filaments 11, 12 are connected to the electronic circuit 16 on the front surface 14 substantially close to the at least one opening 4, 5, 6, 7, such that at least 5% and at most 30%, preferably at most 20% of the respective length of each flexible LED filament 11, 12 of the at least one flexible LED filament is arranged on the first side 1 of the printed circuit board 13.

[0065] Since the least one flexible LED filament 11, 12 is partly arranged on the second side 2 of the printed circuit board 13, extends through the at least one opening 4, 5, 6, 7 from the first side 1 to the second side 2 of the printed circuit board 13, and is mechanically and electrically connected to the electronic circuit 16 on the front surface 14 of the printed circuit board 13, the LED filament arrangement 10 advantageously separates the illumination function of the LED filament arrangement from electronical and mechanical functions. Hence, the LED filament arrangement improves the light distribution and aesthetic appearance of the flexible LED filaments 11, 12 on the second side 2, because the second side 2 of the printed circuit board 13 only exposes the flexible LED filaments 11, 12 and not the electronic circuit 16 or mechanical connections 61, 71 arranged for powering said flexible LED filaments.

[0066] Since the electronic circuit and mechanical connections are all confined to the first side of the printed circuit board, assembly and modularization is also improved.

[0067] For example, figure 2 depicts schematically a LED filament arrangement 20 that is identical to the LED filament arrangement according to the embodiment of figure 1, but wherein the LED filament arrangement 20 further comprises a housing 21 and a light exit window 22. The light exit window 22 may for example comprise an optical element, such as a lens. The housing 31 further accommodates the printed circuit board, wherein the second side of the printed circuit board is facing the light exit window 22. The LED filament arrangement 20 may for example be a GU10 spot with flexible LED filaments.

[0068] For example, figure 3 depicts schematically a luminaire 30 comprising the LED filament arrangement according to the invention, such as the LED filament arrangement according to the embodiment of figure 1 and / or the embodiment of figure 2. The luminaire is a spotlight with a tubular housing, but may alternatively be any other type of luminaire, such as for example a light panel or a streetlight.

[0069] Figure 4 depicts schematically, by non-limiting example, a LED filament arrangement 40 according to the invention. The LED filament arrangement 40 comprises at least one flexible LED filament providing, in operation, LED filament light. More specifically, the at least one flexible LED filament comprises a number of N flexible filaments. Here, said number is 3. Hence, the LED filament arrangement 40 comprises a first flexible LED filament, 51, a second flexible LED filament 52, and a third flexible LED filament 53.

[0070] The LED filament arrangement further comprises a printed circuit board 43. The printed circuit board 43 comprises a front surface 44 arranged on a first side 58 of the printed circuit board 43 and a back surface 45 arranged on a second side 59 of the printed circuit board 43. The second side 59 is thereby opposite to the first side 58.

[0071] The printed circuit board 43 further comprises an electronic circuit 46 arranged on the front surface 44 of the printed circuit board 43, and configured to convey, in operation, power to the at least one flexible LED filament 51, 52, 53.

[0072] The printed circuit board 43 further comprises at least one opening extending through the printed circuit board 43 from the first side 58 to the second side 59. Here, the at least one opening comprises a first opening 54, a second opening 55, and a third opening 56. The at least one flexible LED filaments 51, 52, 53 extend through said at least one opening 54, 55, 56. Here, the at least one opening 54, 55, 56 consists of slits. Alternatively, said openings may be through-holes.

[0073] More specifically, still referring to figure 4, the first flexible LED filament 51 extends through the first opening 54 and the second opening 55; the second flexible LED filament 52 extends through the second opening 55 and the third opening 56; the third flexible LED filament 53 extends through the third opening 56 and the first opening 54. Hence, two flexible LED filaments extend through each single slit.

[0074] Still referring to figure 4, each flexible LED filament of the at least one flexible LED filament 51, 52, 53 is partly arranged on the second side 59 of the printed circuit board 43. Moreover, each flexible LED filament of the at least one flexible LED filament 51, 52, 53 is mechanically and electrically connected to the electronic circuit 46 on the front surface 44 of the printed circuit board 43.

[0075] Figure 5 depicts schematically, by non-limiting example, a top perspective of a LED filament arrangement 50 according to the invention. The LED filament arrangement 50 comprises a first flexible LED filament 81 and a second flexible LED filament 82 and a printed circuit board 83. The printed circuit board 83 has a triangular shape, albeit not limiting to said shape. The printed circuit board 83 comprises a front surface (not depicted) arranged on a first side (not depicted) of the printed circuit board 83, and a back surface 85 arranged on a second side 92 of the printed circuit board 83, wherein the second side 92 is opposite to the first side (not depicted). The printed circuit board 83 also comprises an electronic circuit (not depicted) on the first surface to convey, in operation, power to the first and second flexible LED filament 81, 82. The printed circuit board 83 also comprises a at least one opening 86, 87, 88, 89. Here the at least one opening is a respective slit 86, 87, 88, 89 in the circumference of the triangular printed circuit board 83. More specifically, said slit 86, 87, 88, 89 is an indentation. Still referring to figure 5, the first flexible LED filament 81 extends through a first slit 86 and a second slit 87, while the second flexible LED filament 82 extends through a third slit 87 and a fourth slit 88. Thereby, the first flexible LED filament is partly arranged on the second side 92 of the printed circuit board 83 and is mechanically and electrically connected to the electronic circuit (not depicted) on the front surface of the printed circuit board. Moreover, albeit optionally, the back surface comprises a light reflectivity value of at least 80% for LED filament light emitted, in operation, by said flexible LED filaments. Said printed circuit board may for example be a metal core printed circuit board.

[0076] The exemplar embodiment provided in figure 5 shows, by non-limiting example, one possible configuration. However, other examples may be envisioned similarly, wherein the number of flexible LED filaments, the shape of the printed circuit board, the shape and location of the openings, and the number of flexible LED filaments extending therethrough, can be envisioned differently in alternative configurations.

[0077] Figure 6 depicts schematically, by non-limiting example, a top perspective and bottom perspective of a LED filament arrangement 600 according to the invention.

[0078] The a LED filament arrangement 600 comprises a printed circuit board 613 and a flexible LED filament 604 having a respective length. The printed circuit board comprises a front surface 614 arranged on a first side 601 of the printed circuit board 613. The printed circuit board 613 comprises a back surface 615 arranged on a second side 602 of the printed circuit board, the second side 602 being opposite to the first side.

[0079] The printed circuit board 613 further comprises an electronic circuit 616 arranged on the front surface 614 of the printed circuit board 613 and configured to convey, in operation, power to the at least one flexible LED filament 604.

[0080] The printed circuit board 613 further comprises at least one opening 618 extending through the printed circuit board from the first side 601 to the second side 602. Here, there is only one opening 618. Said flexible LED filament 604 extends through said one opening 618 and is partly arranged on the second side 602 of the printed circuit board 613. Said flexible LED filament 604 is thereby mechanically and electrically connected to the electronic circuit on the front surface of the printed circuit board. More specifically, the flexible LED filament 604 comprises a main part 605, a first end 606 and a second end 607. The main part 605 of the flexible LED filament 604 is partly arranged on the second side 602 of the flexible printed circuit board 613. The first end 606 and the second end 607 extend both through the same one opening 618, and are arranged on the first side of the printed circuit board 613. The first end 606 and the second end 607 are configured to mechanically and electrically connect the flexible LED filament 604 to the electronic circuit on the front surface of the printed circuit board 613. In a related example, not depicted, the at least one opening may comprises a first opening and a second opening, wherein the first end of the flexible LED filament extends through said first opening, and wherein the second end of said flexible LED filament extends through said second opening. Other examples may be envisioned similarly.

Claims

CLAIMS:

1. A LED filament arrangement (10) comprising a printed circuit board (13) and at least one flexible LED filament (11, 12) having a respective length and providing, in operation, LED filament light; wherein each flexible LED filament comprises a respective main part extending between a first end and a second end; wherein the printed circuit board (13) comprises:- a front surface (14) arranged on a first side (1) of the printed circuit board;- a back surface (15) arranged on a second side (2) of the printed circuit board, the second side (2) being opposite to the first side (1);- an electronic circuit (16) arranged on the front surface (14) of the printed circuit board (13) and configured to convey, in operation, power to the at least one flexible LED filament (11, 12);- at least one opening (4, 5, 6, 7) extending through the printed circuit board (13) from the first side (1) to the second side (2); wherein each flexible LED filament (11, 12) extends through one opening or two openings of the at least one opening (4, 5, 6, 7); wherein the respective main part of each flexible LED filament (11, 12) is partly arranged on the second side (2) of the printed circuit board (13); wherein the first end and the second end of each flexible LED filament (11, 12) are mechanically and electrically connected to the electronic circuit (16) on the front surface (14) of the printed circuit board (13).

2. The LED filament arrangement according to claim 1, wherein the at least one flexible LED filament comprises a number of N flexible LED filaments; wherein the at least one opening comprises between N and 2*N openings.

3. The LED filament arrangement according to claim 2, wherein N > 3.

4. The LED filament arrangement according to any one of the preceding claims, wherein said at least one opening is at least one through-hole and / or slit.

5. The LED filament arrangement according to any one of the preceding claims, wherein at least 70% of the respective length of each flexible LED filament is arranged on the second side of the printed circuit board.

6. The LED filament arrangement according to any one of the preceding claims, wherein at least 5% of the respective length of each flexible LED filament of the at least one flexible LED filament is arranged on the first side of the printed circuit board.

7. The LED filament arrangement according to any one of the preceding claims, wherein the back surface comprises a higher reflectivity for the LED filament light than the front surface of the printed circuit board.

8. The LED filament arrangement according to any one of the preceding claims, wherein the back surface is diffusely reflective.

9. The LED filament arrangement according to any one of the preceding claims, wherein the printed circuit board is a metal core printed circuit board (MCPCB).

10. The LED filament arrangement according to any one of the preceding claims, wherein the LED filament arrangement comprises at least one module arranged on the front surface of the printed circuit board; wherein the at least one module is mechanically and electrically connected to the electronic circuit on the front surface of the printed circuit board; wherein the at least one module comprises one or more of: a driver, a controller, a communications module, and / or a sensor.

11. The LED filament arrangement according to any one of the preceding claims, wherein wherein at least 80% of the respective length of each flexible LED filament of the at least one flexible LED filament is arranged on the second side of the printed circuit board and in between the back surface and a virtual plane parallel to said back surface;wherein said virtual plane is at an offset distance of four times the thickness of a flexible LED filament of the at least one flexible LED filament.

12. The LED filament arrangement according to any one of the preceding claims, wherein at least 80% of the respective length of each flexible LED filament of the at least one flexible LED filament is arranged on the second side of the printed circuit board and in between the back surface and a virtual plane parallel to said back surface; wherein said virtual plane is at an offset distance of at most 60 millimeters from the back surface; wherein the at least one flexible LED filament comprises a plurality of curves in a plane parallel to the back surface, wherein each curve comprises an angle of curvature of at least 45 degrees.

13. The LED filament arrangement according to any one of the preceding claims, wherein each flexible LED filament of the at least one flexible LED filament is mechanically and electrically connected to the electronic circuit at respective connection locations on the front surface of the printed circuit board; wherein each of said respective connection locations is within a respective distance D from an opening of the at least one opening; wherein said distance D is equal to at least a factor two and at most a factor ten of a diameter of the respective flexible LED filament of the at least one flexible LED filament.

14. The LED filament arrangement according to any one of the preceding claims, wherein the LED filament arrangement comprises a housing having a light exit window configured to exit said LED filament light and accommodating the printed circuit board, wherein the second side of the printed circuit board is facing the light exit window.

15. A lamp or a luminaire comprising at least one LED filament arrangement according to any one of the preceding claims.

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